Methods and systems for distributing load transfers in power supply systems

ABSTRACT

A power supply system includes an AC power line with an uninterruptible power supply (UPS) device coupled to receive power from the AC power line. The UPS includes control circuitry that couples power conversion circuitry of the UPS to the AC power line when the available AC power is acceptable. The power supply system also includes a second UPS device coupled to receive power from the AC power line. The second UPS includes a timer delay, such that the control circuitry is configured to couple power conversion circuitry to the AC power line when the available AC power is acceptable, and upon expiration of the timer.

BACKGROUND OF INVENTION

1. Field of Invention

Embodiments of the invention relate generally to power management, andmore specifically to methods and systems for preventing power failurefrom large inrush current simultaneously drawn by multiple power loads.

2. Discussion of Related Art

Today's companies and persons rely on having power more than everbefore. Without power, companies may be unable to manufacture goods, orto operate at all, such as if the company is in the business ofsupplying information over the Internet. Without power, businesses andindividuals may be completely incapacitated regarding criticalactivities, such as making goods, providing services, and transactingpersonal finances (e.g., filing tax returns, and paying bills).

With such a heavy reliance on power, individuals and companiesfrequently need to be able to have power outages corrected in shortorder, and/or have backup power supplies so that their affairs and/orbusinesses are not significantly affected, and/or be notified when powerfails. Correcting power outages typically involves calling a local powercompany to report a power outage and/or troubleshooting a local powersupply/conveyance system, e.g., internal to a company or residence, thathas gone out. Uninterruptible power supplies (UPSs) are often used toprovide backup power in case of a power outage. A UPS provides surgeprotection and backup battery power for electronic systems. Backupbattery power helps prevent loss of data that can occur during ablackout, a brownout (low voltage), or a spike or a surge of electricitythrough the system. UPSs are commonly used on computing equipment toguard against data being lost due to a power outage before the data aresaved. UPSs used with computing equipment also help to guard against aloss in service by providers of information over the Internet, such asby servers, e.g., hosting web pages. UPSs can also help improveavailability of network infrastructure in the home during power outages,protect against data loss on personal computers, etc.

SUMMARY OF INVENTION

A facility that has numerous UPS deployed will back up the power formultiple loads, and a number of UPS will connect to a shared line power.During a power outage all the UPS will continue to supply power to theirloads. When the power returns, typically all UPS will attempt to connectto the line power simultaneously, this will cause a step load increaseon the incoming source as the loads all turn on simultaneously. A largestep load increase could potentially cause the input power to failagain. Generally, having a large number of UPS devices instantaneouslyconnect to any power supply source, such as a back up power generator,can create a sudden step load increase, also referred to as inrushcurrent or input surge current, causing failure in the power supply.

At least one embodiment of the invention provides a power supply systemthat includes an AC power line with a plurality of uninterruptible powersupply (UPS) devices coupled to receive power from the AC power line. Afirst UPS includes control circuitry that couples power conversioncircuitry of the UPS to the AC power line when the available AC power isacceptable. The power supply system also includes a second UPS devicecoupled to receive power from the AC power line. The second UPS includesa timer delay, such that the control circuitry is configured to couplepower conversion circuitry to the AC power line when the available ACpower is acceptable, and upon expiration of the timer.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a system diagram of a power supply system according toprinciples of the invention.

FIG. 2A is a block diagram of an embodiment of a UPS device that may beused in the system of FIG. 1 according to principles of the invention.

FIG. 2B is a block diagram of another embodiment of a UPS device thatmay be used on the system of FIG. 1 according to principles of theinvention.

FIG. 3 is a simplified diagram of a communications network and a UPSconnected to the network.

FIG. 4 is a block diagram of an embodiment of a UPS device that may beused in the system of FIG. 3 according to principles of the invention.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing,” “involving,” and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items.

FIG. 1 illustrates a power supply system according to principles of theinvention. The system includes an AC power line 150 that provides powerwith a first uninterruptible power supply (UPS) 110 device coupled to aload 130. A second UPS device 120 also provides power from the AC powerline 150 to a load 140. The UPS devices 110, and 120 contain controlcircuitry configured to selectively convert and supply power from theexternal AC power source 110 or an internal battery pack (not shown inFIG. 1) to their respective loads 130, 140 with desired voltagecharacteristics (e.g., voltage) as directed by a control circuit ofpower circuitry contained within each UPS. The second UPS device 120further contains a timer delay 120 a, that may delay the switching ofthe power source by the control circuitry.

During a power outage the UPS devices will continue to supply power totheir loads by transferring stored power from the internal battery pack,or other energy storage means, such as a flywheel, or capacitor bank.Upon sensing that the available AC power becomes acceptable, the controlcircuitry of the UPS devices couple power conversion circuitry of theUPS devices 110, 120 to the AC power line 150 when the available ACpower is acceptable. When the power returns, typically all UPS deviceswill attempt to connect to the line power simultaneously, causing a stepload increase on the incoming source as the loads all turn onsimultaneously. This step load increase, also referred to as inrushcurrent or input surge current, may cause the input power to fail again.According to principles of the invention, the second UPS includes atimer delay, such that the control circuitry is configured to couplepower conversion circuitry to the AC power line when the available ACpower is acceptable, and upon expiration of the timer. By staggering theconnections of the UPS devices 110, 120 to the AC power line 150, asudden inrush current may be avoided, thus avoiding an overload of theAC power.

On of ordinary skill in the art will understand that multiple UPSdevices may connect to a single AC power line, and that several off-linedevices may reconnect back to the AC power line simultaneously withoutcausing an overload. With larger numbers of UPS devices, groups of UPSdevices may be reconnected in groups, and at different intervals oftime. In embodiments of the present invention, the timer delay betweenthe connection of a first UPS (or group of UPS devices) and a second UPS(or group of UPS devices) to the power line may be between 8 and 12seconds. The delay is short enough so that it is functionallyimperceptible to users of the system, but significant enough to preventa simultaneous inrush. In other embodiments, other delay times may beused.

The UPS devices may further contain other circuitry, such as batterymonitor units to monitor voltage and temperature of the batteries in thebattery pack, and communication units to provide this information to thecontrol circuit via a controller area network (CAN) bus.

FIG. 2A illustrates a UPS 200 that may be used in connection with thesystem of FIG. 1. UPS 200 includes an AC input 202, a transfer switch204, an output 206, a battery 208, a controller 212, and an inverter214. The UPS 200 can include a battery charger 210, but need not. The ACinput 202 is configured to couple to an AC power source and the output206 is configured to couple to a load. The input 202 provides powerreceived from the AC source to the transfer switch 204 and to thebattery charger 210. The transfer switch 204 receives AC power from theinput 202 or from the inverter 214. The inverter 214 receives DC powerfrom the battery 108 and converts the DC power to AC power and providesthe AC power to the transfer switch 204. The controller 212 determineswhether power is to be provided from the AC input 202 or from theinverter 214 in accordance with allowable tolerances of the system. Thecontroller 212 may further include a timer delay 212 a, for example, asubroutine in an existing software module, a separate programmablesoftware module, a Field Programmable Gate Array (FPGA), or separatehardware device, such that the control circuitry is configured to couplepower conversion circuitry to the AC power line when the available ACpower is acceptable, and upon expiration of a timer. The timer delay maybe programmed as the UPS devices are manufactured, wherein one ofseveral predetermined delay intervals may be selected at the time ofmanufacture. Alternatively, the UPS devices may be configured such thatthe timer delay of each UPS device may be manually programmed orre-programmed to one of several predetermined delay intervals.

FIG. 2B illustrates another UPS 250 configured with a double conversiontopology that may be used in connection with the system of FIG. 1. UPS250 includes an AC input 252, a AC/DC rectifier 254, a switch 256, acontroller 258, a battery 260, a AC/DC inverter 262, a static bypassswitch 264 and an output 266. The AC input 252 is configured to coupleto an AC power source and the output 266 is configured to couple to aload. The input 252 provides power received from the AC source to therectifier 254. The rectifier converts the AC power into DC power. Innormal operations, the UPS 250 charges the battery 260 while supplyingthe output 262 with power via the inverter 262. If the AC-input supplyvoltage goes outside any preset tolerance or if it fails, the UPS canenter a stored energy mode wherein the battery 260 continues to supplypower to the output 262 via the inverter 262. The controller 258determines whether power is to be provided from the AC input 262 or thebattery 260 in accordance with allowable tolerances of the system. Thecontroller 258 may further include a timer delay 258 a, for example, asubroutine in an existing software module, a separate programmablesoftware module, an Field Programmable Gate Array (FPGA), or separatehardware device, such that the control circuitry is configured to couplepower conversion circuitry to the AC power line when available AC poweris acceptable, and upon expiration of a timer. Many UPS systemsemploying a double conversion topology further include a static bypassswitch 264 that allows the AC input to provide power directly to theoutput under certain conditions, such as internal malfunction of theUPS, or load current transients (inrush or fault clearing). One ofordinary skill in the art will recognize that in some embodiments, thestatic bypass switch may also be controlled with a timer delay accordingto principles of the invention.

As with the UPS 200 of FIG. 2A, the timer delay of the UPS 250 in FIG.2B may be programmed as the UPS devices are manufactured, wherein one ofseveral predetermined delay intervals may be selected at the time ofmanufacture. Alternatively, the UPS devices may be configured such thatthe timer delay of each UPS device may be manually programmed orre-programmed to one of several predetermined delay intervals.

While FIGS. 2A and 2B illustrate UPS devices employing two differentpower conversion topologies, one of ordinary skill in the art willunderstand that principles of the present invention are not limited tothose topologies, and may be applied to other UPS conversion topologies,or other power conversion topologies.

In yet another power supply system in accordance with principles of theinvention, UPS devices may be networked together, wherein a networkedinterface or controller may set the delay interval between sensingavailable AC power and reconnecting to the AC power of individual UPSdevices. FIG. 3 illustrates a controller 320 and a UPS device 300 thatmay be used in such a system.

Referring to FIG. 3, an uninterruptible power supply (UPS) monitoringand control system 310 comprises a computer 312, a communication network314, a UPS 300, and UPS-supported equipment including a modem 316 and arouter (or switch or hub) 318. The network 314 is preferably apacket-switched network such as an Ethernet local area network (LAN),although other networks would be acceptable. The UPS 300 is configuredto communicate with the computer 312 via the network 314 directly orthrough the router 318. Thus, in the discussion below, reference tocommunication between a UPS 300 and a computer 312 may be through therouter 318 although the router 318 may not be specifically mentioned.

As shown in FIG. 3, a cable 329 (e.g., a coaxial cable) for datacommunication to an external network such as the Internet is connectedto the modem 316 (e.g., a cable modem). An Ethernet line 332 connectsthe modem 316 with the router 318, possibly passing through surgeprotection circuitry in the UPS 300. A line 333 connects the router 318and the UPS 300 for transferring communications, e.g., commands, fromthe router 318 to the UPS 300. The router 318 is further coupled to thecomputer 312 and the UPS 300 through Ethernet lines of the network 314.The UPS 300 is configured to provide backup power to the equipment 316,318 and to provide information regarding use of the backup power via thenetwork 314 to the computer 312. The computer 312 includes a displayscreen 320 for displaying an interface to show the information regardinguse of the backup power provided by the UPS 300 to a user of thecomputer 312.

Referring to FIG. 4, with further reference to FIG. 3, a UPS 400, thatmay be used as UPS 300 in FIG. 3 includes an AC input 402, a transferswitch 404, an output 406, a battery 408, a controller 412, and aninverter 414. The UPS 400 can include a battery charger 410, but neednot. The AC input 402 is configured to couple to an AC power source andthe output 406 is configured to couple to a load. The input 402 providespower received from the AC source to the transfer switch 404 and to thebattery charger 410. The transfer switch 404 receives AC power from theinput 402 or from the inverter 414. The inverter 414 receives DC powerfrom the battery 408 and converts the DC power to AC power and providesthe AC power to the transfer switch 404. The controller 412 determineswhether power is to be provided from the AC input 402 or from theinverter 414 in accordance with allowable tolerances of the system 400.Depending on the capacity of the battery 408 and the power requirementsof the load, the UPS 400 can provide power to the load during brief ACpower source “dropouts” or for extended power outages. The UPS 400 isexemplary only and not limiting as other UPS configurations can be usedwith embodiments of the invention.

The UPS 400 further includes a processor 416 and a network interface418. The processor 416 may be referred to as a slave processor, orsimply a slave, and the controller 412, that includes a processor, maybe referred to as a master processor, or simply a master. The master 412is configured to monitor data regarding status parameters of the UPS 400and to implement control commands to control operation of the UPS 400.The slave 416 is configured to relay information between the networkinterface 418 and the master processor 412. The master 412 and the slave416 preferably operate without software, instead executing instructionsin firmware. The slave 416 preferably can communicate with the master412 at a rapid rate such as 9600 baud.

Similarly, a UPS employing a double conversion topology as illustratedin connection with FIG. 2B, or other conversion topologies (not shown)may be configured with a network interface and used in place of UPS 400.

The slave processor 416 includes embedded Ethernet capability. Usingembedded Ethernet circuitry may help control the cost of the UPS 400,e.g., to make the UPS 400 desirable for home or small business use.

The master microprocessor 412 is configured to control various aspectsof the UPS 400 independently or in accordance with instructions receivedfrom the slave 416 from the computer 312. The controller 412 isconfigured to determine when battery power is needed and to control thetransfer switch 404 to provide power to the output 406 from either theAC input 402 and/or the battery 408, via the inverter 414, asappropriate. A processor in controller 412 is configured to perform itsvarious functions by reading and executing computer-readable,computer-executable software instructions stored in a memory. The master412 can further receive commands/instructions from the computer 312 viathe network 414, the interface 418, and the slave 416 and controlportions of the UPS 400 to implement the commands. For example, thetimer delay 412 a of the master 412 can be set through the computer 312via the network 414, the interface 418, and the slave 416 such that thedelay interval is programmed to one of several preprogrammed delayintervals.

Because the UPS devices may be networked with a centralized intelligentcontroller (such as computer 312), the centralized controller may keeptrack of the delay intervals of each of the UPS devices within thenetworked power supply system, and take into account those delays whensetting assigning or reassigning timer delays for individual UPS deviceswithin the system, such that the devices powering on the AC line atcertain times are evenly distributed.

The storage systems used in connection with the controllers, processors,or timer delays may typically include a computer readable and writeablenonvolatile recording medium in which signals are stored that define aprogram to be executed by the processor or information stored on or inthe medium to be processed by the program to perform one or morefunctions associated with embodiments described herein. The medium may,for example, be a disk or flash memory. Typically, in operation, theprocessor causes data to be read from the nonvolatile recording mediuminto another memory that allows for faster access to the information bythe processor than does the medium. The invention is not limited to aparticular memory system or storage system.

The computer system may include specially-programmed, special-purposehardware, for example, an application-specific integrated circuit(ASIC). Aspects of the invention may be implemented in software,hardware or firmware, or any combination thereof. Further, such methods,acts, systems, system elements and components thereof may be implementedas part of the computer system described above or as an independentcomponent.

Although computer system 312 is shown by way of example as one type ofcomputer system upon which various aspects of the invention may bepracticed, it should be appreciated that aspects of the invention arenot limited to being implemented on the computer system as shown in FIG.3. Computer system 312 may be a general-purpose computer system that isprogrammable using a high-level computer programming language. Computersystem 312 may be also implemented using specially programmed, specialpurpose hardware.

The processor and operating system together define a computer platformfor which application programs in high-level programming languages arewritten. It should be understood that embodiments of the invention arenot limited to a particular computer system platform, processor,operating system, or network. Also, it should be apparent to thoseskilled in the art that the present invention is not limited to aspecific programming language or computer system. Further, it should beappreciated that other appropriate programming languages and otherappropriate computer systems could also be used.

One or more portions of the computer system may be distributed acrossone or more computer systems coupled to a communications network. Forexample, a computer system that determines available power capacity maybe located remotely from a system manager. These computer systems alsomay be general-purpose computer systems. For example, various aspects ofthe invention may be distributed among one or more computer systemsconfigured to provide a service (e.g., servers) to one or more clientcomputers, or to perform an overall task as part of a distributedsystem. For example, various aspects of the invention may be performedon a client-server or multi-tier system that includes componentsdistributed among one or more server systems that perform variousfunctions according to various embodiments of the invention. Thesecomponents may be executable, intermediate (e.g., IL) or interpreted(e.g., Java) code which communicate over a communication network (e.g.,the Internet) using a communication protocol (e.g., TCP/IP). Forexample, one or more database servers may be used to store device data,such as expected power draw, that is used in designing layoutsassociated with embodiments of the present invention.

It should be appreciated that the invention is not limited to executingon any particular system or group of systems. Also, it should beappreciated that the invention is not limited to any particulardistributed architecture, network, or communication protocol.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1. A power supply system comprising: an AC power line; a firstuninterruptible power supply (UPS) device coupled to receive power fromthe AC power line, the first UPS including control circuitry configuredto couple power conversion circuitry to the AC power line when theavailable AC power is acceptable; a second UPS device coupled to receivepower from the AC power line, the second UPS including a timer delay,and control circuitry configured to couple power conversion circuitry tothe AC power line when the available AC power is acceptable, and uponexpiration of the timer delay.
 2. The power supply system of claim 1wherein the timer delay of the second UPS device is programmable.
 3. Thepower supply system of claim 1 wherein the timer delay of the second UPSdevice is factory programmed.
 4. The power supply system of claim 1wherein the first UPS further includes a timer delay and controlcircuitry further configured to couple to the AC power line uponexpiration of the timer delay of the first UPS.
 5. The power supplysystem of claim 1 further comprising: a plurality of UPS devices coupledto receive power from the AC power line, each UPS including a timerdelay, and control circuitry configured to couple power conversioncircuitry to the AC power line when the available AC power isacceptable, and upon expiration of the timer delay.
 6. The power supplysystem of claim 5 wherein the timer delay of each of the plurality ofUPS devices is set with at least two different delay times.
 7. The powersupply system of claim 5 wherein a delay interval between the timerdelays is set between 8 seconds and 10 seconds.
 8. The power supplysystem of claim 5 further comprising a controller coupled to theplurality of UPS devices and configured to set the timer delays of eachof the plurality of UPS devices to one of at least two different timerdelays.
 9. The power supply system of claim 1 wherein the second UPSdevice is configured with a double converter topology.
 10. A method ofdistributing load transfers within a power supply system, the methodcomprising: detecting acceptable line power of a shared power line at aplurality of uninterruptible power supply (UPS) devices; at a first UPSdevice, coupling power conversion circuitry to the power line at a firsttime after the available power is acceptable; at a second UPS device,coupling couple power conversion circuitry to the power line at a secondtime after the available shared power is acceptable, the second time ata delay interval from the first time.
 11. A power supply systemcomprising: a power line; a first plurality of uninterruptible powersupply (UPS) devices coupled to receive power from the power line, thefirst plurality of UPS devices including a first timer delay and controlcircuitry configured to couple power conversion circuitry to the powerline when the available power is acceptable and at the expiration of thefirst timer delay; a second plurality of UPS devices coupled to receivepower from the power line, the second UPS devices including a secondtimer delay, and control circuitry configured to couple power conversioncircuitry to the power line when the available power is acceptable andat the expiration of the second timer delay, where a delay intervalexists between the first timer delay and the second timer delay.
 12. Thepower supply system of claim 11 wherein the delay interval is between 8seconds and 12 seconds.
 13. The power supply system of claim 11 whereinthe delay interval is 10 seconds.
 14. The power supply system of claim11 further comprising: a controller configured to program the firsttimer delay and the second timer delay.
 15. The power supply system ofclaim 14 wherein the controller is further configured to balancedistribution of UPS devices programmed at the first timer delay and UPSdevices programmed at the second timer delay.
 16. A method ofmanufacturing UPS devices, the method comprising: manufacturing UPSdevices coupled to receive power from an AC power line, the UPS devicesincluding a timer delay, and control circuitry configured to couplepower conversion circuitry to the AC power line when the available ACpower is acceptable, and upon expiration of a delay time of the timerdelay; programming the timer delay of individual UPS devices with one ofa plurality of distinct delay times.